Room Temperature Vulcanizing (RTV) Silicone is a two-part liquid that sets to a flexible rubber. It is ideal for making reusable molds. The GI-1000 blue sets softer than many of the other RTV rubbers so it is easy to use as either an interior or exterior molding material. It is easy to use; just mix Part A with Part B (10 to 1) and pour the mixture into a form and allow it to setup overnight. Presto, you have a flexible mold you can use again and again.